Fluorescenated cyanine dyes when localized in biological membranes will fluoresce in response to a transmembrane electrical potential change. Recently researchers have demonstrated that the membrane potential of human platelets change in response to stimuli such as ADT and thrombin. Our current project is exploring the basics of this technique and the possibility of using this technique to assess platelet function through clinically relevant responses to various physiological and pharmacological stimuli. Basic questions relating to the mechanism of action of these various agents may also be answered.